1. Field of the Invention
The present invention relates to the manufacture of a carbon nanotube and more particularly to a method of and apparatus for manufacturing a vertically aligned carbon nanotube grown by chemical vapor deposition (CVD) on a substrate.
2. Description of the Related Art
In the methods proposed heretofore, a substrate with a catalyst carried thereon is placed in a reaction tube disposed in an annular furnace, and while heating the catalyst, a raw material gas serving as a carbon source is continuously brought into contact with the heated catalyst to thereby synthesize a carbon nanotube grown on the substrate in vertical alignment (see Japanese Patent Laid-open Publication (JP-A) No. 2002-180252, and Chemical Physics Letters, Vol. 385, (2004), pp. 298-303).
To reduce the proposed methods into practice, an apparatus such as shown in FIG. 4 hereof is used. The apparatus is equipped with a substrate P1 with a catalyst carried thereon, a carbon source P2, a reaction tube P3, and an annular furnace P4. In this apparatus, a raw material gas that serves as a carbon source and a carrier gas, such as argon (Ar), are continuously supplied into the reaction tube from an upstream side thereof so that carbon is supplied to the catalyst carried on the substrate and eventually a vertically aligned carbon nanotube is synthesized on the substrate.
The conventional carbon nanotube manufacturing method and apparatus have a problem however as shown in FIG. 5 in that, even when the reaction time is extended to increase the film thickness of the synthesized carbon nanotubes (namely, for the purpose of increasing the length of the carbon nanotubes), the direct proportional relationship between the reaction time and the film thickness peaks out at a certain point of time. This is attributed to the fact that due to a long time reaction, the catalyst becomes deactivated by the effect of a reaction byproduct gas and an excess raw material gas.
Furthermore, continuing the supply of carbon source causes another problem in that most of the carbons are exhausted from the reaction tube before being used in the synthesis of carbon nanotubes. This problem lowers the raw material use efficiency and increases the manufacturing cost of the carbon nanotubes.